A preferred way of carbonating beverages, such as brewed products, is by purifying carbon dioxide on site. Therefore, carbon dioxide streams originating from a fermentation process, such as in a brewery, are often purified and returned to the brewery. Thus, the carbon dioxide generated by the fermentation process is used again in the brewed drink or other carbonated beverages produced at the same site as the fermentation process, is used as a so-called cover gas in the bottlery to prevent entrainment of air or to displace air.
Presently the most commonly used method comprises the steps of: defoaming; washing in a water scrubber; compressing; filtrating through a carbon filter; dehydrating; reboiling and distilling the carbon dioxide stream in order to provide the purified carbon dioxide stream. This method effectively purifies carbon dioxide with a satisfactory yield and purity, but several elements of the process add to the cost of the overall recovery process. First of all, the water used in the water scrubber must be disposed of, moreover the carbon filters and dehydrators must be regenerated routinely, and finally external power must be supplied to the method. The large amount of unit operations in the method requires means for maintaining the pressure over the entire system. Generally, the more unit operations comprised in a system the larger the pressure drop and hence the costs for maintaining the same.
Moreover, the conventional final liquefaction of carbon dioxide requires substantive energy supply. The condensation is typically performed by an ammonia cooled condenser. Also, the liquid carbon dioxide produced must be stored in a storage tank and has to be re-evaporated before being used as cover gas or as carbon dioxide for carbonating the beverages. In the conventional method the system is operated at a pressure of approximately 16 bar corresponding to the pressure of a standard carbon dioxide storage tank in which liquid carbon dioxide is stored before being used.
Operating at—in this context—low pressure is the conventional way in the field for recovering high purity carbon dioxide in food grade quality, mainly because this has been considered most economical for several reasons, such as the purity obtained and the cost of installation.
However, operating at lower pressures requires a very high degree of water removal, as the presence of water in the system will cause problems with the formation of ice or gas hydrates. In addition, condensation of the purified carbon dioxide to provide liquefied carbon dioxide requires a high energy input.
The issue of condensation has been addressed in EP 0194795 A2 wherein a recovery process is described in which impure carbon dioxide from a brewing plant is pressurized and cooled, producing a substantially pure carbon dioxide liquid stream and a stream of gaseous impurities, i.e. non-condensable gases. This is followed by expansion of the pure carbon dioxide liquid stream to provide a liquid and gaseous pure carbon dioxide stream, whereby the liquid carbon dioxide provided is used to liquefy the gaseous stream of the initial compression step. Thus, this method provides a solution in which cooling and liquefaction of carbon dioxide is effected by the expansion and evaporation of substantially pure liquid carbon dioxide. Thereby, internal heat transfer and/or cooling power is utilized to supply energy for a purification step. It is stated that this process reduces the specific and overall power consumption and the heat required for vaporization. However, only when the liquefied carbon dioxide is fully employed and expanded will the method be fully economical. Therefore, this method still requires a large energy input for the condensing of the carbon dioxide. The present invention is a method in which one or more of the above problems of the prior art have been solved.